A spun bond non-woven fabric is a typical example of a non-woven fabric comprising filaments. Such fabric is produced by a method wherein a group of filaments discharged from a spinneret for melt spinning are drawn and stretched by introducing into an air sucker etc., opened, and accumulated on a collecting conveyor to be formed into a filament web. Then the filaments are entangled or thermally adhered by appropriate means. Therefore, since this non-woven fabric comprises filaments, that is, continuous fibers, it is more excellent in the mechanical properties such as tensile strength etc. as compared with a non-woven fabric comprising staple fibers. Moreover, since this non-woven fabric is produced by opening and accumulating the filaments obtained directly by melt spinning, it can be rationally produced as compared with non-woven fabrics obtained by opening and accumulating staple fibers by a dry method or a wet method. In recent years, the production of such non-woven fabrics has radically increased.
Moreover, thermally adhesive conjugated fibers comprising polypropylene or polyester as a high melting point component and high density polyethylene, low density polyethylene, or linear low density polyethylene etc. as a low melting point component conventionally have been known. Such conventional thermal adhesive conjugated fiber is formed into, for example, a non-woven fabric by the method wherein a web is produced and then heated at the temperature above the melting point of the low melting point component to bond each fiber by softening or melting the portion where fibers contact each other. However, these thermal adhesive conjugated fibers are poor in bonding or adhesion to the different kind of materials such as metal, paper, rayon, glass or the like, due to the characteristics of the low melting point component of the fiber. Therefore, when the above mentioned non-woven fabric is used by bonding or adhering to the above mentioned different kinds of materials, or when the composite materials are formed by combining this non-woven fabric with different kinds materials, new binder needs to be used. Furthermore, even when a binder is used, the adhesive property is not always excellent.
Moreover, conventionally, absorbent articles of medical and sanitary materials such as disposable diapers like paper diapers, sanitary napkins and the like have structures so that body fluids such as urine, blood or the like are absorbed and the leaking is prevented. Although the structure of such absorbent articles varies between respective specific embodiments, however, such an absorbent article generally comprises an absorptive core layer for absorbing and retaining body fluids such as urine, blood or the like; a liquid permeable cover of the absorptive core layer for wrapping up the absorptive core layer; a liquid permeable top sheet located at the side of the front surface of the cover of the core layer (the side contacting with the user's skin); and a liquid impermeable back sheet located at the back side of the absorptive core layer (the side opposite to the location where the top sheet is located) to which prevent the absorbed body fluids from leaking outside, or the like. Moreover, some of the absorbent articles have a structure comprising a second sheet at the location between the cover of the absorptive core layer and the top sheet, or the location between the absorptive core layer and the cover of the absorptive core layer. The second sheet is inserted so as to provide any of the functions of: providing cushion property, dispersing body fluid, or preventing the absorbed body fluid from returning to the body side. The function of preventing the body fluid absorbed by the absorptive core layer from returning to the body side applies the principles in which the filling density of fibers of the second sheet is made to be smaller than those of the absorptive core layer, and thereby the fluid is made to be absorbed by the absorptive core layer having the larger fiber filling density by the capillary phenomenon etc. However, it is not particularly limited to this method. Besides the above mentioned structures of the absorbent articles, some of the absorbent articles have multi-layered structures because further sheets are inserted for providing various functions.
As the absorptive core layer, a compressed mixture is used in which, in general, the aggregate of fibers comprising cellulose type fiber such as fluff pulp etc. is combined with a highly water absorptive resin. Further synthetic fibers, if necessary, are additionally mixed and hardened therewith. As the liquid permeable cover for wrapping up the absorptive core layers, tissue paper is usually used. Moreover, as the top sheet, a through air non-woven fabric comprising staple fibers (a non-woven fabric produced by the method in which a part of staple fibers constituting non-woven fabric is adhered by heating with hot air) or an embossed type of non-woven fabric comprising staple fibers (a non-woven fabric produced by the method in which a part of staple fibers constituting non-woven fabric is adhered by passing it between the thermal embossing roll and a roll having a smooth surface) etc. is used. Moreover, as the back sheet, a thermoplastic film is usually used. In general, the thermoplastic film has a large number of minute micropores so as to prevent stuffiness inside in use and to provide ventilation. Moreover, from the view point of improving the plastic-like touch and appearance that are peculiar to such films, or from the viewpoint of improving the strength, the composite comprising a film and a non-woven fabric also is used. And necessary portions between the above mentioned parts of the absorbent article are adhered by using appropriate hot melt type adhesives etc.
However, the hot, melt type adhesives have stickiness, and the adhesive strength is not so strong as the case where adhered by using a pressure sensitive adhesives. Furthermore, if too much hot melt type adhesive is used, clogging in each sheet occurs, thus damaging the ventilation or deteriorating a permeability with respect to body fluid.
As to a non-woven fabric comprising filaments, in order to solve the above mentioned problems, as the component to be used for the thermally adhesive component of the non-woven fabric comprising thermal adhesive conjugated filaments, ethylene-acrylic ester-maleic anhydride copolymer having various kinds of functional groups and exhibiting an excellent adhesive property to various kinds of materials is considered to be used as one component of the conjugated filament. Such resin is excellent in adhesive property with respect to other kinds of materials, but it has a problem such as having a strong stickiness and large friction coefficient.
Therefore, there are the following problems: when filaments discharged from the spinning nozzle holes are drawn by the metallic air sucker, the non-uniformity of fineness occurs due to the friction between filaments and metal or between filaments; or filaments thermally adhere to each other and form a bundle, so that the filaments are not easily opened.
Moreover, since in the ethylene-acrylic ester-maleic anhydride copolymer, various kinds of functional groups are introduced into ethylene copolymer, the ethylene-acrylic ester-maleic anhydride copolymer has the low crystallinity, low melting point property, or low softening point property. In a case where the resin having low crystallinity is used, the time or distance for the resin filament discharged from the spinning nozzle holes in a molten state to become crystallized and solidified, namely the solidification length, becomes remarkably long.
Therefore, in such non-woven fabrics, filaments form bundles due to the friction, and non-uniformity of fineness or poor opening may occur. Moreover, the distance between filaments is short, so that filaments whose solidification length becomes long contact with each other in a molten state. That is, low melting point or a low softening point ethylene-acrylic ester-maleic anhydride copolymer portions contact with each other in a molten state, thus causing so-called filament breakage and deteriorating the operating efficiency.
JP-A-3-287875 discloses a thermal adhesive conjugated fiber in which ethylene-acrylic ester-maleic anhydride copolymer is used as a low melting point component and silicon polymer emulsion is substantially applied to the surface to reduce the friction coefficient of the fiber surface. Therefore, it is thought that if this technique is applied, even if the filament comprising ethylene-acrylic ester-maleic anhydride copolymer is used as a low melting point component, a non-woven fabric which is excellent in uniformity can easily be obtained.
However, in the technique disclosed in JP-A-3-287875, staple fibers are presumed to be used. In this case, in general, a finishing agent such as silicon polymer emulsion is applied to the fiber surface in the form of an aqueous emulsion by miffing with surface active agent. At the time of manufacturing non-woven fabrics comprising filaments, it is when filaments are drawn and stretched by the metallic air sucker that the problems tend to occur. Therefore, a finishing agent such as silicon polymer emulsion needs to be applied between the spinneret and the air sucker. However, there are the following problems: applying such a finishing agent to the group of filaments moving at high speed per se is difficult; the applied liquid is splashed in the air sucker; fibers form bundles due to the surface tension of the aqueous emulsion; and in a case where filaments are opened by providing the same electric charge by corona discharge, chargeability is deteriorated due to the finishing agent so that the opening property actually is deteriorated. In view of the above, it is inadequate to directly produce non-woven fabrics comprising filaments by means of this technique.
In other words, even in a case where this technique disclosed in JP-A-3-287875 is used, the opening property is not sufficient and formation (the uniformity of non-woven fabric) is poor, and the hand feeling such as softness or touch etc. is not sufficient. Consequently, this technique is not suitable for producing the non-woven fabrics comprising filaments.
The object of the present invention is to avoid the above mentioned problems and to provide a non-woven fabric comprising filaments comprising conjugated filaments having an excellent adhesive property. A low temperature adhesive property and an excellent adhesive property to other kinds of materials; providing the resultant non-woven fabric comprising filaments with an excellent hand feeling such as softness or touch etc, and the uniformity of the non-woven fabric; and having a high operating efficiency such as spinning property.
Another object of the present invention is to avoid the above mentioned problems of the conventional absorbent articles and by using the above mentioned non-woven fabric comprising filaments in at least one portion of the absorbent article to provide an absorbent article which is free from clogging, which is excellent in adhesive property, and which is well adhered to other members so that layers constituting the absorbent articles are not peeled off and do not lose shape in use.
The present inventors found that by addition of inorganic powders to at least the first component that is a low melting point component or low softening point component, the inorganic powder is exposed at the surface of filaments, so that minute unevenness is provided on the surface of filaments. As a result, the area where the filaments contact with each other is reduced, and adhesion between the filaments during spinning can be inhibited, so that filament breakage is decreased to thus make the operating efficiency good. It also was found that even if inorganic powder is added, the crystallization temperature of ethylene-acrylic ester-maleic anhydride copolymer hardly increases and the increase in the crystallization is remarkably small, and therefore a non-woven fabric comprising filaments which is excellent in hand feeling such as softness or touch etc. can be obtained without damaging the properties of ethylene-acrylic ester-maleic anhydride copolymer, that is, softness, an excellent adhesion property, low temperature adhesion properties and excellent adhesive property to other kind of materials etc. It also was found that when such non-woven fabric comprising filaments is used for at least a part of the absorbent article, an absorbent article which is free from clogging, is excellent in adhesive property, and is well adhered to other members so that layers constituting the absorbent articles are not peeled off and do not lose shape in use can be obtained.